1. Field of the Invention
This invention is directed to wellbore milling systems and methods; and, in one particular aspect, to such systems and methods for milling through a liner that projects into a lateral wellbore from a main wellbore to re-establish a pathway to the main wellbore.
2. Description of Related Art
The prior art discloses a wide variety of wellbore milling systems and methods and a wide variety of systems and methods for re-establishing a pathway through a main wellbore after lining a lateral wellbore with a liner. Many such prior art systems and methods require a guide for a milling system so that the milling system mills back through the liner rather than entering the liner itself and milling in the wrong location. Without such a guide a lateral liner can be damaged by the wrongly located milling system, and the pathway through the main wellbore will not be re-established.
The present invention, in one aspect, discloses a milling system for milling through a lateral bore liner to re-establish a main wellbore. In one aspect the milling system includes a mill with milling blades dressed with milling matrix material and milling inserts; a tubular string connected to and above the mill; and at least one centralizer, rotating centralizer, stabilizer, rotating stabilizer, coupling bushing or the like through which the tubular string extends, the at least one coupling bushing disposed in the main wellbore above a casing window through which the lateral liner extends into the lateral bore.
In one aspect such a system has a plurality of spaced-apart coupling bushings disposed above the lateral bore which serve to position the milling system and prevent it from entering the lateral liner. Such coupling-bushing will facilitate directing of the milling system in the direction of the main wellbore so that the milling system mills through the liner in the direction of the main wellbore, thereby re-establishing the main wellbore. In one aspect one of the coupling bushings is placed above, and in one aspect near the top of, the window at the beginning of the lateral bore.
In some systems a lateral bore liner is supported by an external casing packer, liner hanger, pack-off liner hanger, or similar support positioned in a main wellbore. A milling system as described above that is introduced into the liner through the main wellbore should not abut or hang up on the top of the support apparatus. To facilitate movement of such a milling system past and through an external casing packer a centering apparatus is releasably connected at the bottom of the milling system. As the milling system approaches the top of the external casing packer, the centering device contacts the top of the external casing packer with the lower end of the milling system centered over the bore into the liner. Further downward force on the string to which the milling system is attached releases the centering device and the milling system enters the liner.
In one aspect of a milling system as described herein a coupling bushing has inner slots from top to bottom and/or external ribs to promote fluid flow through and/or around the coupling bushing. Thus circulation for mill cooling and/or cuttings and debris removal is possible.
In one aspect entry of a liner into a lateral wellbore is facilitated by using a bent sub or a bent member at the end of the liner. Also, an orienting apparatus may be used at the end of the liner.
The present invention also discloses systems and methods for shrouding a main bore/lateral liner interface in areas in which formation may be exposed or unsupported.
The present invention discloses systems and methods for installing a liner in a lateral wellbore, the liner having a preformed window located so that, upon desired emplacement of the liner, the preformed window is located above a main wellbore from which the lateral wellbore extends. In this way the preformed window, in one aspect, is positioned over a diverter or whipstock used to direct the liner into the lateral wellbore. Thus a mill is insertable and movable to and through the preformed window to mill through the diverter or whipstock, re-establishing the main wellbore.
It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious devices and methods for milling through a lateral bore liner to re-establish a main wellbore;
Such systems and methods in which one or more coupling bushings, centralizers, stabilizers, and/or similar items are used on a string to which the milling system is connected to position the milling system and inhibit its undesired entry into a lateral liner; and
Such systems and methods with a centering device releasably connected to the milling system for facilitating its entry into a top opening of a liner in the main wellbore.
It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious systems and methods for shrouding a main wellbore/lateral wellbore interface and excluding formation from entering therein.
It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious systems and methods in which a liner having a preformed window is installed with part of the liner in a lateral wellbore and the preformed window located in a main wellbore from which the lateral wellbore extends.
Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.